1. Field of the Invention
This invention relates generally to an electronic apparatus for facilitating the measurement and recording of time varying electrical signals, and more specifically to an electronic interface circuit which may be operated to null out any steady-state or DC bias on which the time varying signal may be superimposed to thereby allow a more accurate processing or reproduction of the time varying signal component.
II. Discussion of the Prior Art
In various electronic systems, it is desirable to measure, monitor or record electrical signals obtained from a signal generating means. For example, in the field of gas or liquid chromatography, the intelligent signal indicative of a change or variation in transmissivity of light through a medium is, in fact, a relatively minute change in a otherwise large DC bias level. Typically, the intelligence signal may be a few hundredths of a percent of the ordinary bias level. When an attempt is made to record such a low level time varying signal, a difficulty arises because the scale setting of the recording instrument must be maintained at too low a value to produce any meaningful amplification of the time varying component because the corresponding amplification of the DC bias level would tend to overdrive the recorder or other measuring instrument. Thus, a need exists for a suitable interface between a sensing apparatus and a downstream recorder or measuring device so that the DC bias level is effectively removed in a fashion which will not distort the time varying component. Once the DC bias is removed, the time varying signal may be amplified to a desired level compatible with the recording or monitoring equipment.